The term "apparatus for observing a subject" is generally intended to mean an optically aided apparatus for use by a person, such as an operating microscope used in surgery, but is not to be specifically limited to this in the context of the invention.
The term "optical system" is understood more particularly as any optical system enabling a person to visualize a subject of observation, at least indirectly, for instance with increased spatial resolution, in particular by magnification of the image projected on the retina of the eye of this person.
The term "visual field" is understood to be the spatial range observed in which the optical system produces its effect; in the case of a microscope, for example, it is the range observed by the operator and in which the magnification sought is obtained.
More precisely, but not exclusively, the invention relates to a method on the one hand for controlling the displacement of the visual field of the optical system of the apparatus and on the other hand of the adjustment of the focusing of this optical system.
Generally, the visual field of an optical system is defined by a conical surface centered on its optical axis.
The displacement of the visual field relates to the relative displacement between the subject and the optical system along at least one axis substantially perpendicular to the optical axis.
Focusing relates to the adjustment that, by a relative displacement substantially in the direction of observation between the subject and at least one of the elements of the optical system, enables the observer to visualize one of the planes of the visual field, which are generally orthogonal to the optical axis, with a certain definition.
In general, the improvement afforded by these optical systems to one parameter of the range of visual perception is achieved to the detriment of other parameters.
For example, an increase in the optical magnification of the image is accompanied by a shrinkage of the visual field and a lessening of the depth of field.
If the range of visual perception is widened, then the role of oculomotor functions, such as sight orientation and accommodation, is markedly reduced.
Optical apparatus having these particular features, such as microscopes used in surgery, are thus conventionally equipped with various adjusting means, including means for adjusting the position of the visual field, the definition, and the magnification.
It will be appreciated that modifications in adjustment necessitate conscious and voluntary action by the observer.
In the case of a surgical microscope, the decisions of the surgeon must be executed quickly and without error.
Since the person's hands are generally occupied with the manipulation of surgical instruments, he may for example have recourse to some external aid, such as an assistant, but this is expensive, and it involves not only a certain response time but also a relatively major risk of mistakes.
Similarly, to modify the adjustments, the surgeon can use pedal-actuated commands, but this offers limited command possibilities and entails an increased risk of confusion in emergencies.
Vocal command with automatic speech recognition could have been an advantageous solution, except that at the moment it is more oriented to all-or-nothing commands than to continuous commands.
Moreover, in situations of nervous tension, the reliability of vocal recognition is altered because of modifications in the tone of voice or changes in the ambient sound level.